We have found that degranulation of mast cells in the reaction site starts within 30 seconds following intradermal pollen antigen injection in sensitized subjects. Using an improved skin chamber technique, we find antigen-induced local release of histamine within 10 minutes with plateau levels reached by 30-60 minutes. Semiquanitative measurement of iflammatory cells migrating into membrane filters appended to the chamber base shows prominent eosinophilic accumulation induced by antigen within 2 hours. We found that histamine and corticosteroids in vitro suppress human lymphocyte proliferation in likely independent patterns. The increase in serum neutrophil chemotactic activity (NCA) after antigen inhalational challenge is associated with an increase in circulating neutrophils. NCA and serum histamine increases are inhibited by prior treatment with theophylline, terbutaline and steroids. Additional studies to characterize serum fractions and chamber fluid rich in NCA are currently underway.